A method of using a phase varying apparatus for varying the opening and closing timing of an engine valve is adopted as a method for optimizing performance of an automobile engine over its entire velocity range from a low velocity range to a high velocity range. In this specification, “engine performance” widely includes fuel economy performance, engine response, low emission performance, idling stability and the like. The phase varying apparatus can select the optimal valve opening and closing timing in accordance with engine operating conditions such as engine rpm by varying the phase relationship of a crankshaft and a camshaft, thereby immensely improving engine performance.
Patent Publication No. 1 discloses a phase varying apparatus for operating a ring gear and a planetary gear of a planetary gear train using two electromagnetic clutches and the main unit of this phase varying apparatus is directly connected to the camshaft. Since the phase varying apparatus is directly connected to the engine, the phase varying apparatus is installed in an environment easily affected by external disturbances such as engine temperature, ambient temperature, vibration and the like. Therefore, in an ECU (engine control unit) constituting controller, not only conventional PID control but also a sliding mode control of high robustness is employed to appropriately control the valve opening and closing timing.